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Why Do Erasers Get Hard?

why do erasers get hard

So, you just found an old pencil behind your desk, and while the graphite is still good, the eraser has gotten so hard that it is no longer usable. Why do erasers get hard after some time?

Why do rubber erasers that you could once use to delicately erase pencil marks on paper turn into rough rocks? After some time, erasers will turn into hard and rough blocks that can rip through the paper if you use them.

This article will teach you the reasons why erasers can turn into almost unusable stumps. You will also find out if you can still restore them.

Why Do Erasers Get Hard?

There are several reasons why pencil erasers can turn into hard stumps. However, not all types and brands of erasers behave the same way. Here are some of the reasons why erasers become almost unusable when they get a bit too old.

UV Exposure

If you store your erasers in a clear jar placed near the window, and they are exposed to more than an hour of direct sunlight daily, then it is highly likely for them to turn hard. Pencil erasers are typically made from different blends of natural rubber, which makes them somewhat organic.

This means that when a pencil eraser is exposed to direct sunlight, the UV rays will cause the organic components to decompose. This is why some old erasers have considerably shrunk from their original size.

Drying Out

drying out

Another of the usual reasons why erasers get quite hard after some time is that they get a bit dried up. As mentioned earlier, pencil erasers are mostly organic rubber, and rubber contains a bit of water. This bit of moisture is the reason why new erasers are quite pliable and effective at erasing pencil marks.

However, when the erasers are exposed to direct sunlight, or just left alone for many months or years, the moisture in the rubber will eventually evaporate. When the eraser no longer has moisture, the rubber will turn into a solid and rigid block.

There is barely just enough moisture in the eraser to keep it held together. If the moisture is completely removed, the eraser would basically turn into dust.


Just leaving your eraser out in the open air will cause it to oxidize. Rubber, when exposed to oxygen and other reactive gasses in the atmosphere, like ozone, will permanently damage the rubber.

Oxidation will cause the rubber to dry, crack, and fade its color. This means that the eraser will lose its flexibility, which essentially turns the eraser into a small brick.

However, unlike the two other methods, oxidation takes a very long time to happen. Just letting an eraser oxidize will take a couple of years before it will turn hard. On the other hand, direct exposure to sunlight will only take a couple of weeks to turn an eraser into a hard block.

Can You Restore Old Erasers?

Now that you know why do pencil erasers get hard, it is time you learn how to restore them. Unless the eraser has gotten seriously deteriorated, you can still somewhat restore your old erasers so that they would work again.

Here are some methods that are quite easy, yet effective.

Boiling in water

boiling in water

You can reintroduce moisture back into your old erasers by placing them into a small pan of boiling water. Make it more effective by adding a bit of dish soap with moisturizer. Around 10 minutes of boiling should be enough to bring your old erasers back to life.

Using Vegetable Oil

using vegetable oil

Some natural rubber erasers usually use vegetable oil in the manufacturing process. The oil helps keep the rubber soft and supple, which will make the eraser flexible. You can bring an old eraser back to life by brushing the surface with a layer of vegetable oil.

After that, you should allow them to sit for a couple of days. The eraser will absorb the vegetable oil, which will then rejuvenate the rubber contained in the eraser.

Using Ivory Bar Soap

using ivory bar soap

Ivory soap or any similar beauty bar soap contains a lot of moisturizers and you can use them to bring back moisture in old erasers. To use this method, you just need to wash the erasers in warm water and then scrub them using ivory soap.

The fats and moisturizers in the soap will help moisturize the rubber content, which will then restore the eraser to its former glory.


Why do erasers get hard after some time? Many factors cause this to happen, including sun exposure and oxidation. You cannot do anything much about this other than sealing your erasers in an airtight container.

However, since this is not that feasible, there are ways to bring them back to their original condition somewhat. Take care of your erasers and other drawing tools and they will serve you well for many years to come.

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